1. Field of the Invention
(Enzyme Inhibitor)
The present invention concerns an inhibitor containing pyrroloquinoline quinone and derivatives thereof as an effective ingredient against aldose reductase, glyoxalase I and reverse transcriptase.
The enzymes as the object of the enzyme inhibitor according to the present invention involve those enzymes selected from the group consisting of aldose reductase, glyoxalase I and reverse transcriptase.
(Aldose Reductase and Inhibitor Therefor)
Aldose reductase is an enzyme that generally acts at the first stage of a sorbitol pathway in which aldose, for example, glucose is converted into sorbitol under the presence of a coenzyme NADPH.sub.2, further, formed into fructose under the action of sorbitol dehydrogenase and NAD, and then transferred into a glycolysis system. The pathway is represented by the following scheme. ##STR2##
It has been known that although glucose is mainly put to a system in which it is converted by means of hexokinase to G-6-P and further decomposed into CO.sub.2 to produce energy in the normal state, activities of hexokinase and sorbitol dehydrogenase are decreased, whereas the activity of aldose reductase is increased in the system of diabetes. Accordingly, glucose metabolism tends to proceed to the sorbitol pathway, by which sorbitol is accumulated within cells to induce diabetic complications such as diabetic cataract, diabetic ventinopathy, diabetic cornea, diabetic nephropathy and diabetic neuropathy. Accordingly, it is possible to prevent and cure diabetic complications by inhibiting the aldose reductase and various aldose reductase inhibitors have been studied and developed, but none of which has yet been put to practical use.
(Glyoxalase I and Inhibitor Therefor)
Generally, glyoxalase I is an enzyme contained in a glyoxalase system and contributes to the first step in a reaction of converting .alpha.-ketoaldehydes into .alpha.-hydroxy acids. It was discovered in 1913 that the glyoxalase system consists of two kinds of enzymes, that is, glyoxalase I and II and, a coenzyme glutathione (GSH). Glyoxalase I (lactoyl glutathionelyase, EC.4.4.1.5) converts hemithioacetal formed from GSH and methyl glyoxal into S-lactoylglutathione and this thioester is hydrolyzed into lactic acid and GSH under the effect of glyoxalase II (hydroxyacylglutathione hydrolase EC.3.1.2.6). ##STR3##
Methyl glyoxal is biologically synthesized in cells from dihydroxyacetone phosphate, glycerol and L-threonine. Methylglyoxal is a cytotoxin although it is formed in the cells. It has been known that methylglyoxal has a potent anti-cancer activity. However, its direct use as the anti-cancer agent has not been realized, because methyl glyoxal is rapidly converted by a glyoxalase system into an inactive S-lactoyl glutathione. It is said that the reaction is particularly remarkable in cancer cells. In view of the above, it has been attempted to accumulate methyl glyoxal by inhibiting glyoxalase I and, in the course of the study, the following two theories have become popular for the mechanism in which the glyoxalase I inhibitor exhibits an anti-cancer activity. One of them is that since glyoxalase I rapidly converts methyl glyoxal having cytotoxicity into lactic acid under the presence of GSH which is considered necessary for cell division, the glyoxalase I inhibitor causes accumulation of methyl glyoxal in cancer cells and, as a result, growth of cancer cells is hindered. The other theory is that since the growth of normal cells is delicately balanced between the growth suppressing effect (methyl glyoxal) and the growth promoting effect (glyoxalase I), the glyoxalase I inhibitor breaks the balance and, as a result, exhibits the anti-cancer activity.
Glyoxalase I inhibitors known so far include, for example, S-substituted GSH, ascorbic acid, lapachol and maltol. Although these inhibitors are effective in vitro, it has often been pointed out that they become invalid by decomposition and exhibit only weak activity of develope toxicity in vivo.
(Reverse Transcriptase and Inhibitor Therefor)
Genetic information is generally transcribed from DNA to RNA and translated into a protein. However, it has been disclosed by Temin that DNA is synthesized from RNA as a template and the genetic information is transcribed from RNA to DNA in RNA type tumour virus. The enzyme having such a type of activity is referred to as a reverse transcriptase. ##STR4##
Presence of such enzymes have been found successively in various RNA type tumour virus recently and those virus having reverse transcriptase are referred to as retrovirus. Typical retrovirus include: Murine leukemia virus (MLV), Rous sarcoma virus (RSV), Avian myeloblastosis virus (AMV), Equine infectious anemia (EIA), Bovine leukemia virus (BLV), Pocine retrovirus, Manson-pfizer monkey virus (MPMV), Human T cell leukemia virus (HTLV), etc. and, particularly, HTLV-III has been noted as AIDS causing virus.
In the duplication of retrovirus, sub group of RNA virus is at first formed for the reverse transcription of genome RNA into DNA. Once the DNA has been formed, the genome of the virus is integrated into the cell genome of a host and utilizes the transcription/translation mechanism of host cell entirely for the purpose of duplication. Once integrated, the virus DNA can not substantially be distinguished from the host DNA by and the virus is stable against attack and can survive as it is as long as the life of the host cell is continued. Then, further new infection is caused. For the prevention and avoidance of new infection, it is necessary to inhibit the reverse transcriptase which plays a main role in the transmission of virus genetic information over a long period of a time, presumably, over the entire life of the host. Accordingly, the inhibitor should be so safe as allowable in view of its toxicity.
Although, tRNA (transfer-RNA) derivatives, Rifampicin derivatives, Carbopol 934, Pyran Copolymer, Phosphonoacetic acid, .beta.-Lapachone, etc. are known as reverse transcriptase inhibitors at present, their in vivo toxicity has often been pointed out in view of their low specificity to the reverse transcriptase or their effectiveness only at a high concentration.
(Problems to be Solved by the Invention)
In view of the present situation as described above, the present inventors have made screening tests for various compounds. Since all of such enzymes are used for diseases requiring their administration for long period of time, it is required to develop those substances that can be administered for a long period of time and exhibit extremely low toxicity and we have a view that it is preferable to screen naturally occurring substances rather than artificially synthesized one. As a result, we have found that pyrroloquinoline quinone and derivatives thereof represented by the formula (I) are natural substances having potent inhibitory activity for aldose reductase, glyoxalase I and reverse transcriptase being safe as well and, as apparent from test examples described later, they have no problems at all in view of the toxicity, that is, they can be used as medical drugs as apparent from the acute toxicity test described later and, as a result of a further study, have accomplished the present invention: ##STR5## where R represents hydrogen or substituted or not substituted alkyl group, alkenyl group, aryl group or aralkyl group which may be substituted, X represents OR' or NR"R"', in which R', R" and R'" represent hydrogen or substituted or not substituted alkyl group, alkenyl group, aryl group or aralkyl group.
Generally, pyrroloquinoline quinone (hereinafter referred to as PQQ) is a novel coenzyme different from conventional coenzyme NAD(P) or flavins for oxydation-reduction and it was initially found as a coenzyme for glucose dehydrogenase of Acinetobactor group. PQQ has a concern with the oxidizing reaction of alcohols, aldehydes, glucose and amines in an organism. Further, its growth promoting effect to a certain kind of micro-organisms, animal cells, plant cells has also been reported. Further, PQQ is also presented in the blood of mammal and, while its vitamin-like physiological activity is guessed, its biological roles has not yet been known at present. However, PQQ and its derivatives constitute the ingredients of an organism and considered to be a stable and non-toxic substance. This is apparent from the result of the acute toxicity test to mouse and rat described later.
TABLE 1 ______________________________________ Acute toxicity test of PQQ tri(dimethylamide) LD.sub.50 (mg/kg) Kind of animal oral subcutaneous ______________________________________ Mouse &gt;5,000 &gt;1,500 Rat &gt;5,000 &gt;1,500 ______________________________________
The PQQ derivative represented by the formula (I) includes an oxidizing quinone and a reducing quinol. The quinone acts as an oxidizing agent and is reduced per se to a quinol. The quinol is again converted into the quinone if an adequate oxidizing agent is present. The quinone can easily form an adduct with alcohol, amine or other nucleophilic agent. ##STR6## (where R and X have the same meanings as described above).
PQQ and its esters can be synthesized by the method of Corey, et al (E. J. Corey and Alfonso Tramontano, J. Am. Chem. Soc., 103, 5599-5600 (1981)). Triamide can be synthesized using PQQ intermediates. That is, as shown by the following reaction scheme, ester (1) as the intermediate product for the synthesis of PQQ is at first hydrolyzed to obtain a carboxylic acid (2). After converting the carboxylic acid (2) into acid chloride (3), it can be treated with dimethylamine to obtain an amide derivative (4). Finally, the amide derivative (4) is oxidized with ceric ammonium nitrate to produce PQQ tri(dimethylamide). ##STR7##
The enzyme inhibitor according to the present invention can be administered either orally or not orally. In the case of oral administration, they can be given in the form of soft or hard capsule, tablet, granule, fine granule and powder. Further, in the case of not-oral administration, they can be given as injection, solution, liquid and supossitory. In addition, slow releasing agent is also effective.
The dosage of the inhibitor according to the present invention is about from 0.1 to 300 mg/kg/day, preferably, from 0.2 to 200 mg/kg/day while different depending on the type, method of administration, symptom and age of patient, etc. It is preferably administered portionwise for 1 to 4 times and, preferably, 1 to 2 times per day.
For formulating the effective ingredient according to the present invention, surface active agent, shaping agent, lubricant, taste conditioner, odor conditioner, colorant, perfumes, preservation agent, suspending agent, wetting agent, film forming substance, coating aid and like other substance are appropriately used in accordance with ordinary manner. Further, it may be used optionally in combination with other inhibitors and medicines.
Test examples and examples will be described below for showing the inhibitory effect of the compound according to the present invention against aldose reductase, glyoxalase I and reverse transcriptase.